1. Field of the Invention
The present invention relates to layer 2 and layer 3 switching of data packets in a nonlocking network switch configured for switching data packets between subnetworks.
2. Background Art
Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) enabling network interface devices at each network node to access the network medium.
The Ethernet protocol IEEE 802.3 has evolved to specify a half-duplex media access mechanism and a full-duplex media access mechanism for transmission of data packets. The full-duplex media access mechanism provides a two-way, point-to-point communication link between two network elements, for example between a network node and a switched hub.
Switched local area networks are encountering increasing demands for higher speed connectivity, more flexible switching performance, and the ability to accommodate more complex network architectures. For example, commonly-assigned U.S. Pat. No. 5,953,335 discloses a network switch configured for switching layer 2 type Ethernet (IEEE 802.3) data packets between different network nodes; a received data packet may include a VLAN (virtual LAN) tagged frame according to IEEE 802.1 q protocol that specifies another subnetwork (via a router) or a prescribed group of stations. Since the switching occurs at the layer 2 level, a router is typically necessary to transfer the data packet between subnetworks.
Efforts to enhance the switching performance of a network switch to include layer 3 (e.g., Internet protocol) processing may suffer serious drawbacks, as current layer 2 switches preferably are configured for operating in a non-blocking mode, where data packets can be output from the switch at the same rate that the data packets are received. Newer designs are needed to ensure that higher speed switches can provide both layer 2 switching and layer 3 switching capabilities for faster speed networks such as 100 Mbps or gigabit networks.
However, such design requirements risk loss of the non-blocking features of the network switch, as it becomes increasingly difficult for the switching fabric of a network switch to be able to perform layer 3 processing at the wire rates (i.e., the network data rate). For example, switching fabrics in layer 2 switches merely need to determine an output port for an incoming layer 2 data packet. Hence, conventional layer 2 switches can perform an address table lookup for switching information merely by searching the address table using a MAC address as a key. For example, a hash function may be performed on a 48-bit MAC address to generate a hash key having a less number of bits, for example, 4 bits. The hash key is then used for accessing an address table configured for storing bin entries and heap entries.
FIG. 1 is a diagram illustrating an address table 100 storing bin entries 102 and heap entries 104. The bin entries serve as an index for a range of heap entries 104, where the heap entries 104 assigned to a given bin entry (e.g., 102) have the same hash key generated for the respective MAC addresses. Each heap entry 104 includes a MAC address field 105, a switching information field 106 that includes switching information for the corresponding MAC address field 105, and a next entry field 108 that specifies the next heap entry 104 belonging to the corresponding bin entry 102, effectively forming a linked list of heap entries 104 for each of the bin entries 102. If the hash key is a 4-bit value, then the address table 102 would include up to sixteen bin entries 102 that could be addressable by the corresponding hash key value. Hence, a switching logic generates a hash key from a MAC address, identifies one of the bin entries based on the hash key, and performs a sequential search of the heap entries 104 belonging to be identified bin entry for the appropriate MAC address. Use of the bin entries 102 for searching of the heap entries 104 provides the advantage of reduced search times, since only the heap entries 104 belonging to a given bin entry 102 need to be searched, as opposed to searching the entire address table 100 as a linked list for a given MAC address.
Layer 3 processing, however, requires not only searching of layer 3 switching information based on an Internet Protocol (IP) address, but also may require additional processing to associate a MAC address to an IP address. Hence, the address table 100 of FIG. 1 and the stored switching information 106 would need to be duplicated for IP address lookup operations because multiple keys (MAC address and IP address) would be necessary to perform layer 3 processing. Consequently, the amount of address table space necessary to add layer 3 processing would be dramatically increased, substantially increasing the cost of the layer 3 switch.
There is a need for an arrangement that enables a network switch to provide layer 2 switching and layer 3 switching capabilities for 100 Mbps and gigabit links without blocking of the data packets.
There is also a need for an arrangement that enables a network switch to provide layer 2 switching and layer 3 switching capabilities with minimal address table sizes to reduce size and cost of the network switch.
There is also a need for an arrangement that enables a switching module of a network switch to perform layer 3 processing using a shared table having both layer 2 and layer 3 address information and switching information.
These and other needs are attained by the present invention, where a network switch includes a switching module having a shared address table storing address entries for both layer 2 and layer 3 address search operations for layer 2 and layer 3 processing. The shared address table is configured for storing in each address entry two key entries, and two pointer fields, enabling each address entry of the shared address table to logically belong to two separate and independent tables for search purposes.
One aspect of the present invention provides a method in a network switch. The method includes receiving a first layer 2 frame at a network switch port, the first layer 2 frame including a layer 2 address and a layer 3 address. The method also includes searching for the layer 2 address in a table having a plurality of table entries, each table entry configured for storing layer 2 and layer 3 address information and a corresponding switching decision. The method also includes searching for the layer 3 address in the table. The searching of the layer 2 and layer 3 addresses from the same table reduces the overall memory space required, since the same table can be used to share data for layer 2 and layer 3 switching operations. Hence, the same table can be used for multiple independent searches.
Another aspect of the present invention provides an integrated network switch configured for executing layer 3 switching decisions. The integrated network switch includes network switch ports, each configured for receiving a layer 2 frame including a Media Access Control (MAC) address and an Internet Protocol (IP) address. The integrated network switch also includes a switching module having a shared address table configured for storing in each table entry a MAC address field, an IP address field, and a switching information field for the corresponding MAC address field and IP address field. The switching module is configured for searching the shared address table using one of the MAC address and the IP address as search keys for the MAC address field and the IP address field, respectively. Use of the shared address table for both MAC address searching and IP address searching eliminates the necessity for duplicating switching information in separate address tables. Hence, each table entry within the shared address table can store all relevant information necessary for performing layer 2 or layer 3 switching for a given network node, for example MAC address, IP address, and switching information, minimizing the memory storage requirements for a layer 3 switching in an integrated network switch.
Additional advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the present invention may be realized and attained by means of instrumentalities and combinations particularly pointed in the appended claims.